Amino acids must be supplied to the fetus by the placenta to meet fetal metabolic needs both for growth and catabolism. The overall objective of this research is to understand the mechanism and regulation of amino acid transfer from mother to fetus. Work will be directed towards characterization of the pathways by which the human placenta takes up amino acids from maternal blood and study of their mechanism and regulation. In vitro incubation procedures and kinetic analysis will be used to obtain quantitative data which can be related to measurements of fetal utilization and in vivo placental amino acid transfer. A preliminary completed study has developed procedures for incubation of human placental tissue, demonstrated the feasibility of such an approach, and discovered an important characteristic of vitro placental uptake of a model amino acid. These procedures will be applied more broadly to the study of the following aspects of placental amino acid uptake; 1) characterization of the specificity and capacity of pathways, 2) study of their alteration during in vitro incubation, 3) investigation of their control by potential physiologic regulatory substances. Quantitative data on transport pathways will be compared with measurements of fetal utilization and in vivo placental amino acid transfer.